Mössbauer Effect ofEr166in Erbium Orthochromite

The hyperfine structure of the Mössbauer resonance in ErCr${\mathrm{O}}_3$ has been studied from 4 to 40°K. At the lowest temperature, a well-resolved hfs pattern is obtained; from this the moment of the ordered ${\mathrm{Er}}^{3+}$ ion can be determined to be $6.2{\mu }_{\beta }$. At higher temperatures, relaxation effects smear the spectrum, and the data have been analyzed using a model in which the Kramers doublet which is the lowest Stark level of ${\mathrm{Er}}^{3+}$ is split by a molecular field coming from both the Cr and Er sublattices. Above the $T_N\left(\mathrm{Er}\right)$, the relaxation rate follows an Orbach process, and below $T_N$ the rate is roughly constant, with $\tau \approx 2\times {10}^{-10\mathrm{}}$ sec. The first excited Stark level was found to lie about 47°K above the ground Kramers doublet.